This invention relates generally to the field of corrosion resistant linings and coatings made with certain organic monoliths and mortars. More specifically, it relates to the process of bonding acid catalyzed furan and phenolic resin based linings and coatings to portland cement concrete or metal substrates.
There are essentially two types of organic resin based monoliths and mortars used in corrosion resistant coatings and linings. First are products based on furan resin solutions; second are products based on phenolic resin solutions. These solutions are combined with a powder portion prior to use. The powder consists mainly of inert fillers, such as sand, silica, clay, carbon, barite, etc., plus small amounts of acid catalysts, which include, for example, a variety of inorganic and organic acids and some organic acid anhydrides and chlorides. The particular type of catalyst is selected mainly to achieve the desired hardening and setting time for the installed monoliths and mortars. The hardening time is adjusted from 15 minutes to a few hours. The products are either used as monolithic corrosion resistant coatings and membranes or as mortars for installing corrosion resistant brick linings.
Furan and phenolic monoliths and mortars, when properly hardened, are highly resistant to most strong acids and bases and to most solvents. They are widely used, therefore, as materials of construction in the chemical industry and also in other industries where corrosive conditions are encountered (e.g. power plants, steel mills, paper industry). The products are used in many different places, for instance, reaction vessels, floors, trenches, pits, catch basins, etc.
With all their usefulness, both furan and phenolic products are afflicted with a serious drawback when used with certain substrates. A monolith or a mortar should adhere tightly to its substrate to become an integrated part of the structure. In many cases a tight bond is essential for the proper function of an installed lining. The two most common substrates, i.e., the surface of structural parts to be lined or coated, are portland cement concrete and carbon steel. Neither furan nor phenolic products will adhere to these materials. The reason for this phenomenon is that the acidic compounds used for curing the cements and mortars are true catalysts, i.e., they are not used up or transformed but stay in the matrix as acids. Enough of the acid slowly bleeds out at the resin cement-substrate interface to react with either the steel or the portland cement. Both steel and portland cement are acid soluble and the reaction products formed at the interface destroy the initial bond. Because of the adhesion loss, furan and phenolics are not used in many applications where they would be superior in all other respects. In some cases, primers based on epoxy resins, polyesters and phenolic resins have been used. However, these primers are seldom used because the epoxides and polyesters require the mixing of two or more components, have a limited pot life, and are fairly expensive. Phenolic primers are hard to apply.
Another problem associated with the use of resin monoliths and mortars, especially the furans, is that they are subject to a considerable shrinkage at curing. The forces generated, especially at the layer thicknesses required for a corrosion resistant lining or coating, are tremendous and can lead to breakage of the bond between mortar and primer.
Single component primer materials have now been found which greatly improve the adhesion of acid catalyzed phenolic and furan resin coatings to metal and portland cement substrates which are easy to apply and which provide a long lasting, bonded coating system.